Light detection device

ABSTRACT

A photodetecting device includes a semiconductor substrate, a plurality of avalanche photodiodes each including a light receiving region disposed at a first principal surface side of the semiconductor substrate, the avalanche photodiodes being arranged two-dimensionally at the semiconductor substrate, and a through-electrode electrically connected to a corresponding light receiving region. The through-electrode is provided in a through-hole penetrating through the semiconductor substrate in an area where the plurality of avalanche photodiodes are arranged two-dimensionally. At the first principal surface side of the semiconductor substrate, a groove surrounding the through-hole is formed between the through-hole and the light receiving region adjacent to the through-hole. A first distance between an edge of the groove and an edge of the through-hole surrounded by the groove is longer than a second distance between the edge of the groove and an edge of the light receiving region adjacent to the through-hole surrounded by the groove.

TECHNICAL FIELD

The present invention relates to a photodetecting device.

BACKGROUND ART

Known photodetecting devices include a semiconductor substrate includinga first principal surface and a second principal surface that opposeeach other (see, for example, Patent Literature 1). The photodetectingdevice described in Patent Literature 1 includes a plurality ofavalanche photodiodes operating in Geiger mode and through-electrodeselectrically connected to the corresponding avalanche photodiodes. Theplurality of avalanche photodiodes are two-dimensionally arranged on thesemiconductor substrate. Each avalanche photodiode includes a lightreceiving region disposed at the first principal surface side of thesemiconductor substrate. The through-electrode is disposed in athrough-hole penetrating through the semiconductor substrate in thethickness direction.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Publication No.2015-61041

SUMMARY OF INVENTION Technical Problem

The object of an aspect of the present invention is to provide aphotodetecting device in which the aperture ratio is ensured, and aninflow of a surface leakage electric current to the avalanche photodiodeis reduced, and structural defects are less likely to occur around thethrough-hole in the semiconductor substrate.

Solution to Problem

As a result of researches and studies, the present inventors have newlyfound the following facts.

When a photodetecting device includes a plurality of avalanchephotodiodes, a through-electrode is placed in a first area where theplurality of avalanche photodiodes are two-dimensionally arranged, forexample, in order to shorten the wiring distance from the avalanchephotodiode. When the through-electrode is disposed outside of the firstarea, the wiring distance between the avalanche photodiode and thethrough-electrode is large, and the difference in the wiring distancesbetween the avalanche photodiodes is large, as compared with when thethrough-electrode is disposed in the first area. The wiring distance isrelated to the wiring resistance, the parasitic capacitance, and thelike, and affects the detection accuracy of the photodetecting device.

The through-hole where the through-electrode is arranged becomes a deadspace for photodetection. Therefore, when the through-electrode isdisposed in the first area, an effective area for photodetection issmall, as compared with when the through-electrode is disposed outsideof the first area. That is, the aperture ratio may decrease. When theaperture ratio decreases, photodetection characteristics of thephotodetecting device are deteriorated.

In order to suppress the reduction of the aperture ratio, it isdesirable that the dead space is as small as possible. For example, theaperture ratio is ensured by reducing the distance between the avalanchephotodiode and the through-hole (through-electrode). When the distancebetween the avalanche photodiode and the through-hole is small, asurface leakage electric current flows easily from the through-hole tothe avalanche photodiode, as compared with when the distance between theavalanche photodiode and the through-hole is large. Consequently, thismay adversely affect the detection accuracy in the photodetectingdevice.

Therefore, the present inventors keenly studied a configuration in whichthe aperture ratio is ensured, and the inflow of the surface leakageelectric current to the avalanche photodiode is reduced.

The present inventors have found a configuration in which a groovesurrounding the through-hole at the first principal surface of thesemiconductor substrate is formed in an area between the through-holeand a light receiving region of an avalanche photodiode adjacent to thethrough-hole. In this configuration, the groove surrounding thethrough-hole is formed in the area between the through-hole and thelight receiving region of the avalanche photodiode adjacent to thethrough-hole, and therefore, even when the distance between the lightreceiving region and the through-electrode (through-hole) is small, aflow of a surface leakage electric current from the through-hole to theavalanche photodiode is reduced.

The present inventors also found that a new problem arises when a groovesurrounding the through-hole is formed in the semiconductor substrate.The groove surrounding the through-hole is formed in a narrow areabetween the through-hole and the light receiving region. For thisreason, a structural defect may occur in the area between the groove andthe through-hole surrounded by the groove in the semiconductorsubstrate. The structural defect is, for example, cracking or chippingof the semiconductor substrate. When a first distance from an edge ofthe groove to an edge of the through-hole surrounded by the groove isequal to or less than a second distance from the edge of the groove tothe edge of the light receiving region adjacent to the through-holesurrounded by the groove, a structural defect is likely to occur, ascompared with when the first distance is longer than the seconddistance.

The present inventors found a configuration in which the first distanceis longer than the second distance. According to this configuration,when the distance between the edge of the light receiving region and theedge of the through-hole adjacent to the light receiving region issmall, and a groove surrounding the through-hole is formed between thelight receiving region and the through-hole adjacent to the lightreceiving region in the semiconductor substrate, a structural defect isunlikely to occur in the area between the groove and the through-holesurrounded by the groove in the semiconductor substrate.

An aspect of the present invention is a photodetecting device includinga semiconductor substrate including a first principal surface and asecond principal surface opposing each other, a plurality of avalanchephotodiodes operating in Geiger mode, and a through-electrode. Each ofthe plurality of avalanche photodiodes includes a light receiving regiondisposed at the first principal surface side of the semiconductorsubstrate, and the avalanche photodiodes are arranged two-dimensionallyon the semiconductor substrate. The through-electrode is electricallyconnected to a corresponding light receiving region. Thethrough-electrode is provided in a through-hole penetrating through thesemiconductor substrate in a thickness direction in an area where theplurality of avalanche photodiodes are arranged two-dimensionally. Atthe first principal surface side of the semiconductor substrate, agroove surrounding the through-hole is formed between the through-holeand the light receiving region adjacent to the through-hole. A firstdistance between an edge of the groove and an edge of the through-holesurrounded by the groove is longer than a second distance between theedge of the groove and an edge of the light receiving region adjacent tothe through-hole surrounded by the groove.

In the photodetecting device according to the aspect, at the firstprincipal surface side of the semiconductor substrate, the groovesurrounding the through-hole is formed in the area between thethrough-hole and the light receiving region adjacent to thethrough-hole, and therefore, the aperture ratio is ensured, and the flowof surface leakage electric current to the avalanche photodiode isreduced. Since the first distance is longer than the second distance, astructural defect is less likely to occur around the through-hole in thesemiconductor substrate.

In the photodetecting device according to the aspect, each avalanchephotodiode may include a first semiconductor region of a firstconductivity type located at the first principal surface side of thesemiconductor substrate, a second semiconductor region of a secondconductivity type located at the second principal surface side of thesemiconductor substrate, a third semiconductor region of the secondconductivity type located between the first semiconductor region and thesecond semiconductor region and having a lower impurity concentrationthan the second semiconductor region, and a fourth semiconductor regionof the first conductivity type formed in the first semiconductor regionand having a higher impurity concentration than the first semiconductorregion. In which case, the fourth semiconductor region may be the lightreceiving region, and a bottom surface of the groove may be constitutedby the second semiconductor region. In this embodiment, the bottomsurface of the groove is deeper than the third semiconductor region.Therefore, even when charges are generated in the area surrounded by thegroove in the semiconductor substrate, this suppresses movement of thecharges generated in the area to the avalanche photodiode. Since thebottom surface of the groove is formed in the semiconductor substrate,i.e., the groove does not reach the second principal surface of thesemiconductor substrate, the semiconductor substrate will not beseparated at the position of the groove. Therefore, in the manufacturingprocess of the photodetecting device, the semiconductor substrate iseasily handled.

In the photodetecting device according to the aspect, each avalanchephotodiode may include a first semiconductor region of a firstconductivity type located at the first principal surface side of thesemiconductor substrate, a second semiconductor region of the firstconductivity type located at the second principal surface side of thesemiconductor substrate and having a higher impurity concentration thanthe first semiconductor region, a third semiconductor region of a secondconductivity type formed at the first principal surface side of thefirst semiconductor region, and a fourth semiconductor region of thefirst conductivity type formed in the first semiconductor region to bein contact with the third semiconductor region, and having a higherimpurity concentration than the first semiconductor region. In whichcase, the third semiconductor region may be the light receiving region,and a bottom surface of the groove may be constituted by the secondsemiconductor region. In this embodiment, the bottom surface of thegroove is deeper than the third semiconductor region. Therefore, evenwhen charges are generated in the area surrounded by the groove in thesemiconductor substrate, this suppresses movement of the chargesgenerated in the area to the avalanche photodiode. Since the bottomsurface of the groove is formed in the semiconductor substrate, i.e.,the groove does not reach the second principal surface of thesemiconductor substrate, the semiconductor substrate will not beseparated at the position of the groove. Therefore, in the manufacturingprocess of the photodetecting device, the semiconductor substrate iseasily handled.

The photodetecting device according to the aspect may include anelectrode pad disposed on the first principal surface and electricallyconnected to the through-electrode. In which case, when viewed from adirection perpendicular to the first principal surface, the electrodepad may be located in an area surrounded by the groove and spaced apartfrom the groove. In this embodiment, when a configuration is employed inwhich the groove is filled with metal, a parasitic capacitance generatedbetween the electrode pad and the metal in the groove is reduced.

In the photodetecting device according to the one aspect, when viewedfrom a direction perpendicular to the first principal surface, an areasurrounded by the groove may have a polygonal shape, and the lightreceiving region may have a polygonal shape. When the area surrounded bythe groove and the light receiving region have polygonal shapes, it ispossible to employ a configuration in which the area surrounded by thegroove and the light receiving region are arranged in such manner that aside of the area surrounded by the groove is along a side of the lightreceiving region. In the photodetecting device adopting thisconfiguration, the dead space is small and the aperture ratio is high.

In the photodetecting device according to the aspect, when viewed from adirection perpendicular to the first principal surface, an opening ofthe through-hole may have a circular shape, and an insulating layer maybe arranged on the inner peripheral surface of the through-hole. Whenthe insulating layer is arranged on the inner peripheral surface of thethrough-hole, the through-electrode and the semiconductor substrate areelectrically insulated from each other. When there is a corner at theopening of the through-hole, a crack may be formed at the corner of theinsulating layer when the insulating layer is formed. Since thethrough-hole has a circular shape when viewed from a directionperpendicular to the first principal surface, cracks tend not to begenerated in the insulating layer when the insulating layer is formed.Therefore, in this embodiment, electrical insulation between thethrough-electrode and the semiconductor substrate is ensured.

In the photodetecting device according to the aspect, the plurality ofavalanche photodiodes may be arranged in a matrix. In which case, thethrough-hole may be formed in each area surrounded by four mutuallyadjacent avalanche photodiodes of the plurality of avalanchephotodiodes. The through-hole may be provided with the through-electrodeelectrically connected to the light receiving region of one of the fourmutually adjacent avalanche photodiodes. The groove may be formed in anarea between the through-hole and the light receiving region of each ofthe four mutually adjacent avalanche photodiodes. In this embodiment,since the wiring distance between the through-electrode and the lightreceiving region electrically connected to the through-electrode isrelatively short, it is unsusceptible to influence by the wiringresistance and the parasitic capacitance. Therefore, this suppressesdegradation of the detection accuracy of the photodetecting device.

When viewed from a direction perpendicular to the first principalsurface, the light receiving region may have a polygonal shape. In whichcase, when viewed from a direction perpendicular to the first principalsurface, the groove may extend along a side adjacent to thethrough-hole, of a plurality of sides of the light receiving region ofeach of the four avalanche photodiodes adjacent to the through-hole. Inthis embodiment, the groove extends along the side of the lightreceiving region, and therefore, a configuration in which the distancebetween the through-hole and the light receiving region is short can beemployed even when the through-hole is formed in each area surrounded bythe four adjacent avalanche photodiodes. The photodetecting device thatemploys this configuration has a smaller dead space and a higheraperture ratio.

Advantageous Effects of Invention

An aspect of the present invention provides a photodetecting device inwhich the aperture ratio is ensured, and an inflow of a surface leakageelectric current to the avalanche photodiode is reduced, and astructural defect is less likely to occur around the through-hole in thesemiconductor substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic perspective view illustrating a photodetectingdevice according to an embodiment.

FIG. 2 is a schematic plan view illustrating a semiconductorphotodetecting element.

FIG. 3 is a schematic enlarged view illustrating the semiconductorphotodetecting element.

FIG. 4 is a diagram for describing a cross-sectional configuration alongline IV-IV illustrated in FIG. 2.

FIG. 5 is a schematic plan view illustrating a mounting substrate.

FIG. 6 is a circuit diagram of the photodetecting device.

FIG. 7 is a diagram for describing a cross-sectional configuration of aphotodetecting device according to a modification of the embodiment.

FIG. 8 is a schematic plan view illustrating a modification of asemiconductor photodetecting element.

FIG. 9 is a schematic plan view illustrating a modification of asemiconductor photodetecting element.

FIG. 10 is a schematic plan view illustrating a modification of asemiconductor photodetecting element.

FIG. 11 is a schematic plan view illustrating a modification of asemiconductor photodetecting element.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be hereinafter described indetail with reference to the accompanying drawings. In the description,the same reference numerals are used for the same elements or elementshaving the same functions, and redundant descriptions thereabout areomitted.

First, a configuration of a photodetecting device 1 according to thepresent embodiment will be described with reference to FIG. 1 to FIG. 4.FIG. 1 is a schematic perspective view illustrating the photodetectingdevice according to the present embodiment. FIG. 2 is a schematic planview illustrating semiconductor photodetecting elements. FIG. 3 is aschematic enlarged view illustrating a semiconductor photodetectingelement. FIG. 4 is a diagram for describing a cross-sectionalconfiguration along line IV-IV illustrated in FIG. 2.

As illustrated in FIG. 1, the photodetecting device 1 includes asemiconductor photodetecting element 10A, a mounting substrate 20, and aglass substrate 30. The mounting substrate 20 opposes the semiconductorphotodetecting element 10A. The glass substrate 30 opposes thesemiconductor photodetecting element 10A. The semiconductorphotodetecting element 10A is disposed between the mounting substrate 20and the glass substrate 30. In the present embodiment, a plane inparallel with each principal surface of the semiconductor photodetectingelement 10A, the mounting substrate 20, and the glass substrate 30 isthe XY-axis plane, and a direction perpendicular to each principalsurface is the Z-axis direction.

The semiconductor photodetecting element 10A includes a semiconductorsubstrate 50A having a rectangular shape in a plan view. Thesemiconductor substrate 50A is made of Si and is an N type (secondconductivity type) semiconductor substrate. The semiconductor substrate50A includes a principal surface 1Na and a principal surface 1Nb thatoppose each other.

As illustrated in FIG. 2, the semiconductor photodetecting element 10Aincludes a plurality of avalanche photodiodes APD and a plurality ofthrough-electrodes TE. The plurality of avalanche photodiodes APD aretwo-dimensionally arranged on the semiconductor substrate 50A. In thepresent embodiment, the avalanche photodiodes APD are arranged in amatrix. In the present embodiment, the row direction is X-axis directionand the column direction is Y-axis direction. The avalanche photodiodesAPD are arranged with an equal distance on a straight line when theavalanche photodiodes APD are viewed from each of the X-axis directionand the Y-axis direction.

Each avalanche photodiode APD includes a light receiving region S1 andoperates in Geiger mode. The light receiving region S1 is arranged at aprincipal surface 1Na side of the semiconductor substrate 50A. Asillustrated in FIG. 6, the avalanche photodiodes APD are connected inparallel in such a manner that a quenching resistor R1 is connected inseries with each avalanche photodiode APD. A reverse bias voltage isapplied to each avalanche photodiode APD from a power supply. The outputelectric current from each avalanche photodiode APD is detected by asignal processing unit SP. The light receiving region S1 is a chargegenerating region (a photosensitive region) configured to generatecharges in response to incident light. That is, the light receivingregion S1 is a photodetecting region.

The glass substrate 30 includes a principal surface 30 a and a principalsurface 30 b that oppose each other. The glass substrate 30 has arectangular shape in a plan view. The principal surface 30 b opposes theprincipal surface 1Na of the semiconductor substrate 50A. The principalsurface 30 a and the principal surface 30 b are flat. The glasssubstrate 30 and the semiconductor photodetecting element 10A areoptically connected by an optical adhesive OA. The glass substrate 30may be formed directly on the semiconductor photodetecting element 10A.

A scintillator (not illustrated) may be optically connected to theprincipal surface 30 a of the glass substrate 30. In which case, thescintillator is connected to the principal surface 30 a by an opticaladhesive. The scintillation light from the scintillator passes throughthe glass substrate 30 and is incident on the semiconductorphotodetecting element 10A.

The mounting substrate 20 includes a principal surface 20 a and aprincipal surface 20 b that oppose each other. The mounting substrate 20has a rectangular shape in a plan view. The principal surface 20 aopposes the principal surface 1Nb of the semiconductor substrate 50A.The mounting substrate 20 includes a plurality of electrodes arranged onthe principal surface 20 a. These electrodes are arranged correspondingto the through-electrodes TE.

The side surface 1Nc of the semiconductor substrate 50A, the sidesurface 30 c of the glass substrate 30, and the side surface 20 c of themounting substrate 20 are flush with each other. That is, in the planview, the outer edge of the semiconductor substrate 50A, the outer edgeof the glass substrate 30, and the outer edge of the mounting substrate20 match each other. The outer edge of the semiconductor substrate 50A,the outer edge of the glass substrate 30, and the outer edge of themounting substrate 20 do not have to match each other. For example, inthe plan view, the area of the mounting substrate 20 may be larger thanthe area of each of the semiconductor substrate 50A and the glasssubstrate 30. In which case, the side surface 20 c of the mountingsubstrate 20 is located outside, in the XY-axis plane direction, of theside surface 1Nc of the semiconductor substrate 50A and the side surface30 c of the glass substrate 30.

Next, the structure of the semiconductor photodetecting element 10A willbe described with reference to FIG. 2 and FIG. 3. FIG. 2 is a viewillustrating the semiconductor photodetecting element 10A that is viewedfrom the direction perpendicular to the principal surface 1Na of thesemiconductor substrate 50A (Z-axis direction). FIG. 3 illustrates anarea where the groove is formed.

One avalanche photodiode APD constitutes one cell in the semiconductorphotodetecting element 10A. Each avalanche photodiode APD includes onelight receiving region S1. That is, the semiconductor photodetectingelement 10A includes a plurality of light receiving regions S1. Thelight receiving region S1 has a polygonal shape when viewed from theZ-axis direction. The light receiving region S1 of the semiconductorphotodetecting element 10A has a substantially regular octagonal shapewhen viewed from the Z-axis direction.

The plurality of light receiving regions S1 are two-dimensionallyarranged when viewed from the Z-axis direction. In the presentembodiment, the plurality of light receiving regions S1 are arranged ina matrix. The light receiving regions S1 are arranged with an equaldistance on a straight line when viewed from each of the X-axisdirection and the Y-axis direction. In the present embodiment, the lightreceiving regions S1 are arranged with a pitch of 100 μm. In thesemiconductor photodetecting element 10A, two adjacent light receivingregions S1 are arranged in such a manner that one side of an octagonshape opposes each other.

Each avalanche photodiode APD includes an electrode E1. The electrode E1is arranged on the principal surface 1Na side of the semiconductorsubstrate 50A. The electrode E1 is provided along the contour of thelight receiving region S1 and has an octagonal ring shape.

The electrode E1 includes a connected portion C that is electricallyconnected to the light receiving region S1. The connected portions C areprovided on the four sides of the light receiving region S1. Theconnected portions C are provided alternately on the sides of the lightreceiving region S1. In which case, the detection accuracy of the signalfrom the light receiving region S1 is ensured. As illustrated in FIG. 3,the connected portion C includes a first end portion Ela and a secondend portion E1 b and extends on the XY-axis plane from the outer edgetoward the center of the light receiving region S1. As also illustratedin FIG. 4, the electrode E1 extends in the Z-axis direction at thesecond end portion E1 b. Accordingly, a step is formed at the positionof the second end portion Eb in the electrode E1. The electrode E1extends from the step in the direction opposite to the center of thelight receiving region S1. The electrode E1 includes a third end portionE1 c that is electrically connected to the wiring F.

As illustrated also in FIG. 4, the wiring F extends from the third endportion E1 c in the direction opposite to the center of the lightreceiving region S1. The wiring F electrically connects the electrode E1and an electrode pad 12. The wiring F is located above the semiconductorsubstrate 50A outside of the light receiving region S1. The wiring F isformed above the semiconductor substrate 50A with an insulating layer L1interposed therebetween.

The electrode E1 and a through-electrode TE are made of metal. Theelectrode E1 and the through-electrode TE are made of, for example,aluminum (Al). When the semiconductor substrate is made of Si, copper(Cu) is used as an electrode material instead of aluminum. The electrodeE1 and the through-electrode TE may be integrally formed. The electrodeE1 and the through-electrode TE are formed, for example, by sputtering.

The semiconductor photodetecting element 10A includes a plurality of thethrough-electrodes TE and a plurality of the electrode pads 12. Eachthrough-electrode TE is electrically connected to a correspondingavalanche photodiode APD. Each electrode pad 12 is electricallyconnected to a corresponding through-electrode TE. The electrode pad 12is electrically connected to the electrode E1 through the wiring F. Theelectrode pad 12 is arranged on the principal surface 1Na. Eachthrough-electrode TE is electrically connected to the light receivingregion S1 through the electrode pad 12, the wiring F, and the electrodeE1. The electrode pad 12 is positioned in an area (the inner area of thegroove 13) AR1 surrounded by the groove 13 when viewed from the Z-axisdirection, and the electrode pad 12 is away from the groove 13.

The through-electrode TE is arranged for each avalanche photodiode APD.The through-electrode TE penetrates through the semiconductor substrate50A from the principal surface 1Na side to the principal surface 1Nbside. The through-electrode TE is disposed in a through-hole THpenetrating through the semiconductor substrate 50A in the thicknessdirection (Z-axis direction). The through-hole TH is located in the areawhere multiple avalanche photodiodes APD are arranged two-dimensionally.In the semiconductor substrate 50A, a plurality of the through-holes THare formed.

The opening of the through-hole TH is located in the XY-axis plane andhas a circular shape when viewed from the Z-axis direction. Thecross-sectional shape of the through-hole TI in the cross section inparallel with the XY-axis plane is a circular shape. The semiconductorphotodetecting element 10A includes the insulating layer L2 on the innerperipheral surface of the through-hole TH. The through-electrode TE isarranged in the through-hole TH with the insulating layer L2 interposedtherebetween.

The plurality of through-holes TH are arranged in such a manner that thecenters of the openings are located in a matrix when viewed from theZ-axis direction. In the present embodiment, the row direction is X-axisdirection and the column direction is Y-axis direction. The plurality ofthrough-holes TH are arranged in such a manner that the centers of theopenings are arranged with an equal distance on a straight line whenviewed from each of the X-axis direction and the Y-axis direction. Thethrough-holes TH are arranged with a pitch of 100 μm.

Each of the plurality of through-holes TH is formed in an areasurrounded by four mutually adjacent avalanche photodiodes APD, of theplurality of avalanche photodiodes APD. In the through-hole TH, thethrough-electrode TE is arranged, the through-electrode TE beingelectrically connected to the light receiving region S1 of one of thefour mutually adjacent avalanche photodiodes APD. That is, thethrough-electrode TE is electrically connected to the light receivingregion S1 of the avalanche photodiode APD of one of the four avalanchephotodiodes APD surrounding the through-hole TH in which thethrough-electrode TB is arranged.

The plurality of through-holes TH and the plurality of light receivingregions S1 are arranged in such a manner that, when viewed from theZ-axis direction, four through-holes TH surround one light receivingregion S1 and four light receiving regions S1 surround one through-holeTH. The through-hole TH and the light receiving region S1 arealternately arranged in directions crossing the X-axis and the Y-axis.

Each of four sides of the eight sides of the light receiving region S1opposes a side of an adjacent light receiving region S1, and theremaining four sides oppose the adjacent through-holes TH. Onethrough-hole TH is surrounded by one side of the four light receivingregions S1 when viewed from the Z-axis direction. The connected portionsC are provided on four sides opposing the through-hole TH, of the eightsides of the light receiving region S1.

The principal surface 1Na of the semiconductor substrate 50A includesthe light receiving region S1, an intermediate area S2, and an openingperipheral area S3. The opening peripheral area S3 is an area located atthe periphery of the opening of the through-hole TH of the principalsurface 1Na. The intermediate area S2 is an area excluding the lightreceiving region S1 and the opening peripheral area S3 in the principalsurface 1Na.

A groove 13 is formed in an intermediate area S2 between the lightreceiving regions S1 of the four mutually adjacent avalanche photodiodesAPD and the through-hole TH surrounded by these avalanche photodiodesAPD. The groove 13 extends along the sides adjacent to the through-holeTH, of the plurality of sides of the light receiving regions S1 of thefour mutually adjacent avalanche photodiodes APD when viewed from theZ-axis direction. In the semiconductor photodetecting element 10A, thegroove 13 surrounds the entire circumference of the through-hole TH whenviewed from the Z-axis direction. The area AR1 surrounded by the groove13 is a substantially square when viewed from the Z-axis direction. Onethrough-hole TH is formed in any given area AR1.

A groove 14 is formed in the intermediate area S2 between two mutuallyadjacent light receiving regions S1. The groove 14 extends along twoopposing sides of two adjacent light receiving regions S1 when viewedfrom the Z-axis direction. The groove 14 connects the grooves 13surrounding different through-holes TH. In the semiconductorphotodetecting element 10A, the entire circumference of the lightreceiving region S1 is surrounded by the grooves 13 and 14. In one areaAR2, one light receiving region S1 is provided. The area AR2 hassubstantially the same regular octagonal shape as the shape of the lightreceiving region S1. The areas AR1 and AR2 have a polygonal shape whenviewed from the 2-axis direction.

The groove 14 extends in a straight line in the area between twoadjacent light receiving regions S1. The groove 14 surrounding the twoadjacent light receiving regions S1 is shared by two adjacent lightreceiving regions S1. The groove 14 located in the area between twoadjacent light receiving regions S1 is not only a groove surrounding onelight receiving region S1 abut also a groove surrounding the other lightreceiving region S1.

As illustrated in FIG. 3, a distance β from an edge 13 e of the groove13 to an edge D2 of the through-hole TH surrounded by the groove 13 islonger than a distance α from an edge 13 f of the groove 13 to an edgeD1 of the light receiving region S1 adjacent to the through-hole TH. Inthe present embodiment, the distance α is 5.5 μm and the distance β is7.5 μm. The distance α is the shortest distance from the edge 13 f ofthe groove 13 to the edge DI of the light receiving region S1 adjacentto the through-hole TH when viewed from the Z-axis direction. Thedistance β is the shortest distance from the edge 13 e of the groove 13to the edge D2 of the through-hole TH surrounded by the groove 13 whenviewed from the Z-axis direction.

Next, the cross-sectional configuration of the semiconductorphotodetecting element according the present embodiment will bedescribed with reference to FIG. 4. In FIG. 4, the glass substrate 30and the optical adhesive OA are not illustrated.

Each avalanche photodiode APD includes the light receiving region S1.Each avalanche photodiode APD includes a first semiconductor region 1PAof a P-type (first conductivity type), a second semiconductor region 1NAof an N-type (second conductivity type), a third semiconductor region1NB of an N-type, and a fourth semiconductor region 1PB of P-type.

The first semiconductor region 1PA is located at the principal surface1Na side of the semiconductor substrate 50A. The second semiconductorregion 1NA is located at the principal surface 1Nb side of thesemiconductor substrate 50A. The third semiconductor region 1NB islocated between the first semiconductor region 1PA and the secondsemiconductor region 1NA and has a lower impurity concentration than thesecond semiconductor region 1NA. The fourth semiconductor region 1PB isformed inside of the first semiconductor region 1PA and has a higherimpurity concentration than the first semiconductor region 1PA. Thefourth semiconductor region 1PB is the light receiving region S1. Eachavalanche photodiode APD is configured to include: a P⁺ layer serving asthe fourth semiconductor region 1PB; a P layer serving as the firstsemiconductor region 1PA; an N layer serving as the third semiconductorregion 1NB; and an N⁺ layer serving as the second semiconductor region1NA, which are arranged in this order from the principal surface 1Na.

The first semiconductor region 1PA is located in the intermediate areaS2 when viewed from the Z-axis direction and is positioned to surroundthe fourth semiconductor region 1PB (light receiving region S1).Although not illustrated in the drawing, the first semiconductor region1PA is also located in the intermediate area S2 between two mutuallyadjacent light receiving regions S1 when viewed from the Z-axisdirection. The intermediate area S2 of the semiconductor substrate 50Ais configured to include: a P layer serving as the first semiconductorregion 1PA; an N layer serving as the third semiconductor region 1NB;and an N⁺ layer serving as the second semiconductor region 1NA, whichare arranged in this order from the principal surface 1Na except theportion where the grooves 13, 14 are formed.

The inner surface 13 b of the groove 13 is formed by the same N⁺ layeras the second semiconductor region 1NA. On the inner surface 13 b, aninsulating layer 13 c is provided. A filling material 13 a is providedin the area surrounded by the insulating layer 13 c in the groove 13.The filling material 13 a is made of, for example, a material that iseasy to fill and has a high light shielding property. In the presentembodiment, the filling material 13 a is made of tungsten (W). Like theinner surface 13 b, the inner surface of the groove 14 is formed by thesame N layer as the second semiconductor region 1NA. An insulating layer13 c and a filling material 13 a are provided in the groove 14 like thegroove 13. FIG. 4 does not illustrate the groove 14, and the insulatinglayer 13 c and the filling material 13 a provided in the groove 14. Thefilling material 13 a may be made of copper or aluminum instead oftungsten.

The depth of the grooves 13 and 14, i.e., a distance from the principalsurface 1Na to the bottom surfaces of the grooves 13 and 14 in theZ-axis direction (the thickness direction of the semiconductor substrate50A), is longer than a distance in the Z-axis direction from theprincipal surface 1Na to the interface between the second semiconductorregion 1NA and the third semiconductor region 1NB, and shorter than thethickness of the semiconductor substrate 50A. The bottom surface 13 d ofthe groove 13 is constituted by the second semiconductor region 1NA andis located closer to the principal surface 1Nb than the thirdsemiconductor region 1NB.

The semiconductor substrate 50A includes an N-type fifth semiconductorregion INC. The fifth semiconductor region INC is formed between theedge D2 of the through-hole TH and the first semiconductor region 1PAwhen viewed from the Z-axis direction. Like the second semiconductorregion 1NA, the fifth semiconductor region INC is an N⁺ layer with ahigher impurity concentration than the third semiconductor region 1NB.On the principal surface 1Na, an area where the fifth semiconductorregion INC is formed is the opening peripheral area S3. The openingperipheral area S3 of the semiconductor substrate 50A is configured toinclude: an N⁺ layer serving as the fifth semiconductor region INC; andan N⁺ layer serving as the second semiconductor region 1NA, which arearranged in this order from the principal surface 1Na.

The inner peripheral surface (edge D2) of the through-hole TH isconfigured to include the fifth semiconductor region INC and the secondsemiconductor region 1NA, which are arranged in this order from theprincipal surface 1Na. Therefore, a PN junction formed by the firstsemiconductor region 1PA and the third semiconductor region 1NB is notexposed to the through-hole TH.

The avalanche photodiode APD includes an electrode E1. The connectedportion C of the electrode E1 is connected to the fourth semiconductorregion 1PB (light receiving region S1). As described above, theconnected portion C includes the first end portion Ela and the secondend portion E1 b. The electrode E1 includes the third end portion E1 c.

The first semiconductor region 1PA is electrically connected to theelectrode E1 through the fourth semiconductor region 1PB.

The electrode pad 12 is electrically connected to the through-electrodeTE. The through-electrode TE extends to the back side (adjacent to theprincipal surface 1Nb) of the semiconductor substrate 50A. Thethrough-electrode TE is provided with an insulating layer L3 adjacent tothe mounting substrate 20. The through-electrode TE is electricallyconnected to the mounting substrate 20 through a bump electrode BE onthe back side of the semiconductor substrate 50A. The electrode E1 andthe mounting substrate 20 are electrically connected to each otherthrough the wiring F, the electrode pad 12, the through-electrode TE,and the bump electrode BE. The fourth semiconductor region 1PB iselectrically connected to the mounting substrate 20 through theelectrode E1, the wiring F, the electrode pad 12, the through-electrodeTE, and the bump electrode BE. The bump electrode BE is made of, forexample, solder.

The bump electrode BE is formed on the through-electrode TE extending onthe principal surface 1Nb with an under bump metal (UBM), notillustrated, interposed therebetween. The UBM is made of a material withexcellent electrical and physical connection with the bump electrode BE.The UBM is formed by, for example, an electroless plating method. Thebump electrode BE is formed by, for example, a method of mounting asolder ball or a printing method.

Next, the mounting substrate according to the present embodiment will bedescribed with reference to FIG. 5. FIG. 5 is a schematic plan view ofthe mounting substrate. As illustrated in FIG. 5, the mounting substrate20 includes a plurality of electrodes E9, a plurality of quenchingresistors R1, and a plurality of signal processing units SP. Themounting substrate 20 constitutes an application specific integratedcircuit (ASIC). The quenching resistor R1 may be located at thesemiconductor photodetecting element 10A instead of the mountingsubstrate 20.

Each electrode E9 is electrically connected to the bump electrode BE.The electrode E9 is made of a metal just like the electrode E1 and thethrough-electrode TE. The electrode E9 is made of, for example,aluminum. The material constituting the electrode E9 may be copperinstead of aluminum.

Each quenching resistor R1 is disposed on the principal surface 20 aside. One end of the quenching resistor R1 is electrically connected tothe electrode E9, and the other end of the quenching resistor R1 isconnected to a common electrode CE. The quenching resistor R1constitutes a passive quenching circuit. A plurality of quenchingresistors R1 are connected in parallel to the common electrode CE.

Each signal processing unit SP is located on the principal surface 20 aside. An input terminal of the signal processing unit SP is electricallyconnected to the electrode E9 and an output terminal of the signalprocessing unit SP is connected to the signal line TL. Each signalprocessing unit SP receives an output signal from the correspondingavalanche photodiode APD (semiconductor photodetecting element 10A)through the electrode E1, the through-electrode TE, the bump electrodeBE, and the electrode E9. Each signal processing unit SP processes theoutput signal from the corresponding avalanche photodiode APD. Eachsignal processing unit SP includes a CMOS circuit that converts theoutput signal from the corresponding avalanche photodiode APD into adigital pulse.

Next, the circuit configuration of the photodetecting device 1 will bedescribed with reference to FIG. 6. FIG. 6 is a circuit diagram of thephotodetecting device. In the photodetecting device 1 (semiconductorphotodetecting element 10A), an avalanche photodiode APD is formed by aPN junction formed between the N-type third semiconductor region 1NB andthe P-type first semiconductor region 1PA. The semiconductor substrate50A is electrically connected to an electrode (not illustrated) arrangedon the back side, and the first semiconductor region 1PA is connected tothe electrode E1 through the fourth semiconductor region 1PB. Eachquenching resistor R1 is connected in series with the correspondingavalanche photodiode APD.

In the semiconductor photodetecting element 10A, each avalanchephotodiode APD operates in Geiger mode. In Geiger mode, a reversevoltage (reverse bias voltage) greater than the breakdown voltage of theavalanche photodiode APD is applied to between the anode and the cathodeof the avalanche photodiode APD. For example, a (−) potential V1 isapplied to the anode and a (+) potential V2 is applied to the cathode.The polarities of these potentials are relative to each other, and onepotential may be the ground potential.

The anode is the first semiconductor region 1PA and the cathode is thethird semiconductor region 1NB. When light (photon) is incident on theavalanche photodiode APD, photoelectric conversion is performed insideof the substrate to generate photoelectrons. At an area near the PNjunction interface of the first semiconductor region 1PA, avalanchemultiplication is performed and the amplified electron group movestoward the electrode arranged on the back side of the semiconductorsubstrate 50A. When light (photon) is incident on any cell (avalanchephotodiode APD) of the semiconductor photodetecting element 10A, thelight is multiplied and obtained from the electrode E9 as a signal. Thesignal retrieved from the electrode E9 is input to the correspondingsignal processing unit SP.

As described above, the photodetecting device 1 is configured in such amanner that, on the principal surface 1Na side of the semiconductorsubstrate 50A, the groove 13 surrounding the through-hole TH is formedin the intermediate area S2 between the through-hole TH and the lightreceiving region S1 adjacent to the through-hole TH. Therefore, in theintermediate area S2 between the through-electrode TE and the lightreceiving region S1, the principal surface 1Na of the semiconductorsubstrate 50A is divided. As a result, even if the light receivingregion S1 and the through-electrode TE are close to each other in orderto ensure the aperture ratio of the avalanche photodiode APD, the flowof the surface leakage electric current from the through-electrode TE tothe avalanche photodiode APD is reduced.

The distance β is longer than the distance α. Therefore, structuraldefects tend not to be generated around the through-holes TH in thesemiconductor substrate 50A.

The bottom surface 13 d of the groove 13 is constituted by the secondsemiconductor region 1NA. The bottom surface 13 d of the groove 13 islocated deeper than the third semiconductor region 1NB. Therefore, evenwhen charges are generated in the area surrounded by the groove 13 inthe semiconductor substrate 50A, this suppresses movement of the chargesgenerated in the area to the avalanche photodiode APD. Since the bottomsurface 13 d of the groove 13 is formed in the semiconductor substrate50A, i.e., the groove 13 does not reach the principal surface 1Nb of thesemiconductor substrate 50A, the semiconductor substrate 50A will not beseparated at the position of the groove 13. Therefore, in themanufacturing process of the photodetecting device 1, the semiconductorsubstrate 50A is easily handled.

In the groove 13, a filling material 13 a made of tungsten is provided.Since the electrode pad 12 is spaced apart from the groove 13, theparasitic capacitance generated between the electrode pad 12 and thefilling material 13 a is reduced.

When viewed from the Z-axis direction, the area AR1 and the area AR2have a polygonal shape and the light receiving region S1 has a polygonalshape. When the light receiving region S1 has a circular shape, there isno corner where the electric field concentrates. In the case where thelight receiving region S1 has a circular shape, the dead space generatedbetween the light receiving region S1 and the through-hole TH is large,as compared with when the light receiving region S1 has a polygonalshape. Therefore, it is difficult to ensure the aperture ratio. Theareas AR1 and AR2, and the light receiving region S1 have a polygonalshape. The areas AR1 and AR2 and the light receiving region S1 arearranged in such a manner that the sides of the areas AR1 and AR2 arealong the side of the light receiving region S1. For this reason, thephotodetecting device 1 has a small dead space, and a high apertureratio.

When viewed from the Z-axis direction, the opening of the through-holeTH has a circular shape, and the insulating layer L2 is arranged in theinner peripheral surface of the through-hole TR Since the insulatinglayer L2 is disposed on the inner peripheral surface of the through-holeTH, the through-electrode TE and the semiconductor substrate 50A areelectrically insulate from each other. When there is a corner at theopening of the through-hole TH, a crack may be formed at the corner ofthe insulating layer L2 when the insulating layer L2 is formed. In thepresent embodiment, since the through-hole TH has a circular shape whenviewed from a direction perpendicular to the principal surface 1Na,cracks tend not to be generated in the insulating layer L2 when theinsulating layer L2 is formed. Therefore, in the photodetecting device1, electrical insulation between the through-electrode TE and thesemiconductor substrate 50A is ensured.

The through-electrode TE is electrically connected to the lightreceiving region S1 of avalanche photodiode APD of one of the fourmutually adjacent avalanche photodiodes APD. In which case, since thewiring distance between the through-electrode TE and the light receivingregion S1 electrically connected to the through-electrode TE isrelatively short, it is unsusceptible to influence by the wiringresistance and the parasitic capacitance. Therefore, this suppressesdegradation of the detection accuracy of the photodetecting device 1.

The light receiving region S1 has a polygonal shape when viewed from theZ-axis direction. When viewed from the Z-axis direction, the groove 13extends along the sides adjacent to the through-hole TH1, of theplurality of the sides of the light receiving regions S1 of fouravalanche photodiodes APD adjacent to the through-hole TH. Since thegroove 13 extends along the sides of the light receiving regions S1, thedistance between the through-hole TH and light receiving region S1 canbe configured to be narrow even when the through-hole TH is formed ineach area surrounded by four mutually adjacent avalanche photodiodesAPD. For this reason, the photodetecting device 1 has a small deadspace, and a high aperture ratio.

When the light receiving region S1 has an octagonal shape when viewedfrom the Z-axis direction, the area other than the through-electrode TEin the principal surface 1Na can be efficiently made use of. Therefore,the photodetecting device 1 achieves a configuration having a shortwiring distance between the through-electrode TE and the light receivingregion S1, and the aperture ratio is improved, as compared with in thecase where the light receiving region S1 has other shapes.

When the filling material 13 a disposed in the grooves 13, 14 is made ofa metal, a parasitic capacitance may be generated between the fillingmaterial 13 a and the light receiving region S1. When the value ofparasitic capacitance differs according to the position between thefilling material 13 a and the light receiving region S1, i.e., when thevalue of parasitic capacitance is deviated, the photodetecting accuracyof the avalanche photodiode APD may be reduced. In the photodetectingdevice 1, the grooves 13 and 14 are formed in such a manner that theedges of the grooves 13 and 14 are along the edge D1 of the lightreceiving region S1 when viewed from the Z-axis direction. Therefore,even when a parasitic capacitance is generated between the fillingmaterial 13 a and the light receiving region S1, the value of theparasitic capacitance is less likely to be biased. As a result, theavalanche photodiode APD is less affected by the parasitic capacitance.

The groove 14 surrounding the two adjacent light receiving regions S1 isformed in such a manner that the edge of the groove 14 is along the edgeDI of the light receiving region S1. The groove 14 is shared by twoadjacent light receiving regions S1. Therefore, the avalanche photodiodeAPD is less affected by the parasitic capacitance. Furthermore, the areaof the principal surface 1Na is effectively utilized, so that the lightreceiving regions S1 of the avalanche photodiodes APD are denselyarranged. As a result, not only a reduction of the influence of theparasitic capacitance on the avalanche photodiode APD but also animprovement of the aperture ratio is realized.

Next, a configuration of a photodetecting device according to amodification of the present embodiment will be described with referenceto FIG. 7. FIG. 7 is a diagram for describing a cross-sectionalconfiguration of a photodetecting device according to the modificationof the present embodiment. FIG. 7 illustrates a cross-sectionalconfiguration obtained when the photodetecting device according to thismodification is cut along the plane corresponding to line IV-IVillustrated in FIG. 2. FIG. 7 also does not illustrate the glasssubstrate 30 and the optical adhesive OA. The modification is generallysimilar or the same as the above-described embodiment, but themodification differs from the above-described embodiment in theconfiguration of the avalanche photodiodes APD, as described below.

The photodetecting device according to the present modification includesa semiconductor photodetecting element 10B. The semiconductorphotodetecting element 10B is disposed between the mounting substrate 20and the glass substrate 30. The semiconductor photodetecting element 10Bincludes a semiconductor substrate 50B having a rectangular shape in aplan view. The semiconductor substrate 50B is made of Si and is an Ntype (second conductivity type) semiconductor substrate. Thesemiconductor substrate 50B includes a principal surface 1Na and aprincipal surface 1Nb that oppose each other. The semiconductorphotodetecting element 10B includes a plurality of avalanche photodiodesAPD and a plurality of through-electrodes TE. The plurality of avalanchephotodiodes APD are two-dimensionally arranged on the semiconductorsubstrate 50B. In the present modification, the avalanche photodiodesAPD are arranged in a matrix.

A groove 23 formed in the semiconductor photodetecting element 10B hasthe same configuration as the groove 13 formed in the semiconductorphotodetecting element 10A. The groove 23 is formed in an intermediatearea S2 between the light receiving regions S1 of the four mutuallyadjacent avalanche photodiodes APD and the through-hole TH surrounded bythese avalanche photodiodes APD. The groove 23 extends along the sidesadjacent to the through-hole TH, of the plurality of sides of the lightreceiving regions S1 of the four avalanche photodiodes APD adjacent tothe through-hole TH when viewed from the Z-axis direction. In thesemiconductor photodetecting element 10B, the groove 23 surrounds theentire circumference of the through-hole TH. The area AR1 surrounded bythe groove 23 is substantially square when viewed from the Z-axisdirection. In the present modification, one through-hole TH is alsoformed in any given area AR1.

A groove 14 is formed in the intermediate area S2 between two mutuallyadjacent light receiving regions S1. FIG. 7 does not illustrate thegroove 14. The groove 14 extends along two opposing sides of twoadjacent light receiving regions S1 when viewed from the Z-axisdirection. The groove 14 connects the grooves 23 surrounding differentthrough-holes TH. In the semiconductor photodetecting element 10B, theentire circumference of the light receiving region S1 is surrounded bythe grooves 23 and 14. The area AR2 surrounded by the grooves 23 and 14has substantially the same regular octagonal shape as the shape of thelight receiving region S1. In the present modification, the areas AR1and AR2 have a polygonal shape when viewed from the Z-axis direction.One light receiving region S1 is disposed in any given area AR2.

In the present modification, the groove 14 extends in a straight line inthe area between two adjacent light receiving regions S1. The groove 14surrounding the two adjacent light receiving regions S1 is shared by twoadjacent light receiving regions S1.

As illustrated in FIG. 7, a distance β from an edge 23 e of the groove23 to an edge D2 of the through-hole TH surrounded by the groove 23 islonger than a distance α from an edge 23 f of the groove 23 to an edgeD1 of the light receiving region S1 adjacent to the through-hole TH. Inthe present modification, the distance α is 5.5 μm and the distance β is7.5 μm. The distance α is the shortest distance from the edge 23 f ofthe groove 23 to the edge D1 of the light receiving region S1 adjacentto the through-hole TH when viewed from the Z-axis direction. Thedistance β is the shortest distance from the edge 23 e of the groove 23to the edge D2 of the through-hole TH surrounded by the groove 23 whenviewed from the Z-axis direction.

In the semiconductor photodetecting element 10B, each avalanchephotodiode APD also includes the light receiving region S1. Eachavalanche photodiode APD includes a first semiconductor region 2PA ofP-type (first conductivity type), a second semiconductor region 2PB ofP-type, a third semiconductor region 2NA of N-type, and a fourthsemiconductor region 2PC of P-type.

The first semiconductor region 2PA is located at the principal surface1Na side of the semiconductor substrate 50B. The second semiconductorregion 2PB is located at the principal surface 1Nb side of thesemiconductor substrate 50B, and has a higher impurity concentrationthan the first semiconductor region 2PA. The third semiconductor region2NA is formed at the principal surface 1Na side of the firstsemiconductor region 2PA. The fourth semiconductor region 2PC is formedin the first semiconductor region 2PA to be in contact with the thirdsemiconductor region 2NA and has a higher impurity concentration thanthe first semiconductor region 2PA. The third semiconductor region 2NAis the light receiving region S1. Each avalanche photodiode APD isconfigured to include: an N⁺ layer serving as the third semiconductorregion 2NA; a P layer serving as the fourth semiconductor region 2PC; aP⁻ layer serving as the first semiconductor region 2PA; and a P⁺ layerserving as the second semiconductor region 2PB, which are arranged inthis order from the principal surface 1Na.

The first semiconductor region 2PA is located in the intermediate areaS2 when viewed from the Z-axis direction and is positioned to surroundthe third semiconductor region 2NA that is the light receiving regionS1. Although not illustrated in the drawing, the first semiconductorregion 2PA is also located in the intermediate area S2 between twomutually adjacent light receiving regions S1 when viewed from the Z-axisdirection. The intermediate area S2 of the semiconductor substrate 50Bis configured to include: a P⁻ layer serving as the first semiconductorregion 2PA; and a P⁺ layer serving as the second semiconductor region2PB, which are arranged in this order from the principal surface 1Naexcept the portion where the grooves 23, 14 are formed.

The inner surface 23 b of the groove 23 is formed by the same P⁺ layeras the second semiconductor region 2PB. On the inner surface 23 b, aninsulating layer 23 c is provided. A filling material 23 a is providedin the area surrounded by the insulating layer 23 c in the groove 23.The filling material 23 a is made of, for example, a material that iseasy to fill and has a high light shielding property. In the presentmodification, the filling material 23 a is made of tungsten (W), whichis the same as the filling material 13 a. Like the inner surface 23 b,the inner surface of the groove 14 is formed by the P⁺ layer having ahigher impurity concentration than the first semiconductor region 2PA.An insulating layer 23 c and a filling material 23 a are provided in thegroove 14 like the groove 23. As described above, FIG. 7 does notillustrate the groove 14, and the insulating layer 23 c and the fillingmaterial 23 a provided in the groove 14. The filling material 13 a maybe made of copper or aluminum instead of tungsten.

The depth of the grooves 23 and 14, i.e., a distance from the principalsurface 1Na to the bottom surfaces of the grooves 23 and 14 in theZ-axis direction (the thickness direction of the semiconductor substrateSOB), is longer than a distance in the Z-axis direction from theprincipal surface 1Na to the interface between the first semiconductorregion 2PA and the second semiconductor region 2PB, and shorter than thethickness of the semiconductor substrate 50B. The bottom surface 23 d ofthe groove 23 is constituted by the second semiconductor region 2PB andis located closer to the principal surface 1Nb than the firstsemiconductor region 2PA.

The semiconductor substrate 50B includes a P-type fifth semiconductorregion 2PD. The fifth semiconductor region 2PD is formed between theedge D2 of the through-hole TH and the first semiconductor region 2PAwhen viewed from the Z-axis direction. Like the second semiconductorregion 2PB, the fifth semiconductor region 2PD is a P⁺ layer with ahigher impurity concentration than the first semiconductor region 2PA.On the principal surface 1Na, an area where the fifth semiconductorregion 2PD is formed is the opening peripheral area S3. The openingperipheral area S3 of the semiconductor substrate SOB is configured toinclude: a P⁺ layer serving as the fifth semiconductor region 2PD; and aP⁺ layer serving as the second semiconductor region 2PB, which arearranged in this order from the principal surface 1Na.

The inner peripheral surface (edge D2) of the through-hole TH isconfigured to include the fifth semiconductor region 2PD and the secondsemiconductor region 2PB, which are arranged in this order from theprincipal surface 1Na. Therefore, a PN junction formed by the thirdsemiconductor region 2NA and the fourth semiconductor region 2PC is notexposed to the through-hole TH.

The avalanche photodiode APD includes an electrode E1. The electrode E1is arranged at the principal surface 1Na side of the semiconductorsubstrate 50B. In the present modification, the electrode E1 is providedalong the contour of the light receiving region S1 and has an octagonalring shape.

The electrode E1 includes a connected portion C that is electricallyconnected to the light receiving region S1. In the present modification,as illustrated in FIG. 7, the connected portion C includes a first endportion Ela and a second end portion E1 b. The electrode E1 includes athird end portion E1 c that is electrically connected to the wiring F.

As illustrated in FIG. 7, the wiring F extends from the third endportion E1 c in the direction opposite to the center of the lightreceiving region S1. The wiring F electrically connects the electrode E1and an electrode pad 12. The wiring F is located above the semiconductorsubstrate 50B outside of the light receiving region S1. The wiring F isformed above the semiconductor substrate 50B with an insulating layer L1interposed therebetween.

In the present modification, the electrode pad 12 is also electricallyconnected to the through-electrode TE. The through-electrode TE extendsto the back side (adjacent to the principal surface 1Nb side) of thesemiconductor substrate 50B. The through-electrode TE is provided withan insulating layer L3. The through-electrode TE is electricallyconnected to the mounting substrate 20 via the bump electrode BE. Theelectrode E1 and the mounting substrate 20 are electrically connected toeach other through the wiring F, the electrode pad 12, thethrough-electrode TE, and the bump electrode BE. The third semiconductorregion 2NA is electrically connected to the mounting substrate 20through the electrode E1, the wiring F, the electrode pad 12, thethrough-electrode TE, and the bump electrode BE.

As described above, according to the present modification, on theprincipal surface 1Na side of the semiconductor substrate SOB, thegroove 23 surrounding the through-hole TH is formed in the intermediatearea S2 between the through-hole TH and the light receiving region S1adjacent to the through-hole TH. Therefore, in the intermediate area S2between the through-electrode TE and the light receiving region S1, theprincipal surface 1Na of the semiconductor substrate 50B is divided. Asa result, even if the light receiving region S1 and thethrough-electrode TE are close to each other in order to ensure theaperture ratio of the avalanche photodiode APD, the flow of the surfaceleakage electric current from the through-electrode TE to the avalanchephotodiode APD is reduced.

The distance β is longer than the distance α. Therefore, structuraldefects tend not to be generated around the through-holes TH in thesemiconductor substrate 50B.

The bottom surface 23 d of the groove 23 is constituted by the secondsemiconductor region 2PB. The bottom surface 23 d of the groove 23 islocated deeper than the first semiconductor region 2PA. Therefore, evenwhen charges are generated in the area surrounded by the groove 23 inthe semiconductor substrate SOB, this suppresses movement of the chargesgenerated in the area to the avalanche photodiode APD. Since the bottomsurface 23 d of the groove 23 is formed in the semiconductor substrateSOB, i.e., the groove 23 does not reach the principal surface 1Nb of thesemiconductor substrate 50B, the semiconductor substrate 50B will not beseparated at the position of the groove 23. Therefore, in themanufacturing process of the photodetecting device according to thepresent modification, the semiconductor substrate 50B is easily handled.

Next, the configurations of modifications of the semiconductorphotodetecting element will be described with reference to FIG. 8 toFIG. 11. FIG. 8 to FIG. 11 are schematic plan views illustrating themodifications of the semiconductor photodetecting element.

Semiconductor photodetecting elements 10C, 10D, 10E, and 10F aredisposed between a mounting substrate 20 and a glass substrate 30. Likethe semiconductor photodetecting element 10A, the semiconductorphotodetecting elements 10C, 10D, 10E, and 10F include a semiconductorsubstrate 50A having a rectangular shape in a plan view. Thesemiconductor photodetecting elements 10C, 10D, 10E, and 10F include aplurality of avalanche photodiodes APD and a plurality ofthrough-electrodes TE.

In the semiconductor photodetecting element 10C as illustrated in FIG.8, a groove 13 is formed in an intermediate area S2 between thethrough-hole TH and the light receiving region S1 adjacent to thethrough-hole TH. The groove 13 surrounds the through-hole TH. The groove13 is not formed in an area arranged with the wiring F that electricallyconnects the through-electrode TE and the light receiving region S1 whenviewed from the Z-axis direction. The groove 13 surrounds thethrough-hole TH in such a state that the groove 13 is divided by thearea where the wiring F is arranged when viewed from the Z-axisdirection.

In the semiconductor photodetecting element 10D as illustrated in FIG.9, a groove 13 is formed in the intermediate area S2 between athrough-hole TH and the light receiving region S1 adjacent to thethrough-hole TH. The groove 13 surrounds the through-hole TH.

FIG. 2 and FIG. 9 are scaled differently. The size of the electrode pad12 of the semiconductor photodetecting element 10D is the same as thesize of the electrode pad 12 of the semiconductor photodetecting element10A.

The through-holes TH and the light receiving regions S1 aretwo-dimensionally arranged. Each pitch of the through-hole TH and thelight receiving region S1 is less than those of the semiconductorphotodetecting element 10A. In the semiconductor photodetecting element10D, the through-hole TH and the light receiving region S1 are arrangedin a one-to-one relationship to achieve a higher resolution than thesemiconductor photodetecting element 10A. Each pitch of the lightreceiving region S1 and the through-hole TH is, for example, 70 μM.

In the semiconductor photodetecting element 10D, the groove 13 surroundsthe through-hole TH, like the semiconductor photodetecting element 10A.Like the semiconductor photodetecting element 10A, the groove 14 alsoextends along two opposing sides of two adjacent light receiving regionsS1 when viewed from the Z-axis direction. The groove 14 connects thegrooves 13 surrounding different through-holes TH. In the semiconductorphotodetecting element 10D, the entire circumference of the lightreceiving region S1 is also surrounded by the grooves 13 and 14.

In the semiconductor photodetecting element 10D, each pitch of thethrough-electrode TE and the light receiving region S1 is smaller thanthose of the semiconductor photodetecting element 10A. In thesemiconductor photodetecting element 10D, the groove 14 surrounding thetwo adjacent light receiving regions S1 is formed in such a manner thatthe edge of the groove 14 is along the edge D1 of the light receivingregion S1, like the semiconductor photodetecting element 10A. The groove14 is shared by two adjacent light receiving regions S1.

Therefore, the avalanche photodiode APD is less affected by theparasitic capacitance. In addition, the area of the principal surface1Na is effectively utilized, and the light receiving regions S1 of theavalanche photodiodes APD are densely arranged.

It is difficult to reduce the size of the through-electrode TE becauseof problems in machining accuracy or ensuring electrical connection. Inorder to reduce the parasitic capacitance generated between theelectrode pad 12 and the filling material 13 a in the grooves 13 and 14,the grooves 13 and 14 are separated from the electrode pad 12. In orderto improve the aperture ratio, the light receiving region S1 has apolygonal shape.

Under these conditions, the light receiving region S1 of thesemiconductor photodetecting element 10D has a polygonal shape differentfrom the light receiving region S1 of the semiconductor photodetectingelement 10A. More specifically, the light receiving region S1 of thesemiconductor photodetecting element 10D has a polygonal shape in whichthe length of the side opposing the adjacent light receiving region S1is shorter than the length of the side opposing the adjacentthrough-hole TH.

With this configuration, in the semiconductor photodetecting element10D, the resolution is higher than that of the semiconductorphotodetecting element 10A, and the semiconductor photodetecting element10D achieves a higher aperture ratio. The parasitic capacitancegenerated among the avalanche photodiode APD, the filling material 13 a,and the electrode pad 12 is reduced.

In the semiconductor photodetecting element 10E illustrated in FIG. 10,the groove 13 is formed in the intermediate area S2 between thethrough-hole TH and the light receiving region S1 adjacent to thethrough-hole TH. The groove 13 surrounds the through-hole TH. FIG. 2 andFIG. 10 are scaled differently. The size of the electrode pad 12 of thesemiconductor photodetecting element 10E is the same as the size of theelectrode pad 12 of the semiconductor photodetecting element 10A.

In the semiconductor photodetecting element 10E, the pitch of thethrough-hole TH is the same as the pitch of the through-hole TH of thesemiconductor photodetecting element 10A, the pitch of the lightreceiving region S1 is the same as the pitch of the light receivingregion S1 of the semiconductor photodetecting element 10A. Thethrough-hole TH and the light receiving region S1 are arranged in such amanner that the through-hole TH and the light receiving region S1 arearranged in a one-to-one relationship. Like the light receiving regionS1 of the semiconductor photodetecting element 10A, the light receivingregion S1 of the semiconductor photodetecting element 10E has asubstantially octagonal shape. The area of the light receiving region S1of the semiconductor photodetecting element 10E is smaller than the areaof the light receiving region S1 of the semiconductor photodetectingelement 10A. In the semiconductor photodetecting element 10E, twogrooves 14 extend in the area between two mutually adjacent lightreceiving regions S1. One groove 14 surrounds one light receiving regionS1 and the other groove 14 surrounds the other light receiving regionS1. That is, the groove 14 is not shared by two adjacent light receivingregions S1.

The groove 13 of the semiconductor photodetecting element 10E surroundsthe through-hole TH in such a state that the grooves 13 are separated inthe row direction and the column direction in which the through-holes THare arranged. Like the groove 14 of the semiconductor photodetectingelement 10A, the groove 14 of the semiconductor photodetecting element10E also extends along two opposing sides of two adjacent lightreceiving regions S1 when viewed from the Z-axis direction. The groove14 connects the grooves 13 surrounding different through-holes TI. Inthe semiconductor photodetecting element 10E, the entire circumferenceof the light receiving region S1 is also surrounded by the grooves 13and 14.

In order to reduce the influence of the parasitic capacitance on theavalanche photodiode APD, the grooves 13 and 14 are formed in such amanner that the edges of the grooves 13 and 14 are along the edge D1 ofthe light receiving region S1. It is difficult to reduce the size of thethrough-electrode TE because of problems in machining accuracy orensuring electrical connection. In order to reduce the parasiticcapacitance generated between the electrode pad 12 and the fillingmaterial 13 a in the grooves 13 and 14, the grooves 13 and 14 areseparated from the electrode pad 12.

In the semiconductor photodetecting element 10E, since two grooves 14extend in the area between two mutually adjacent light receiving regionsS1, the crosstalk between the light receiving regions S1 is reduced to alevel lower than the semiconductor photodetecting element 10A.Therefore, in the semiconductor photodetecting element 10E, thecrosstalk between the light receiving regions S1 is reduced to a levellower than the semiconductor photodetecting element 10A, and theparasitic capacitance generated between the avalanche photodiode APD,the filling material 13 a, and the electrode pad 12 is reduced.

In the semiconductor photodetecting element 10F illustrated in FIG. 11,the groove 13 is formed in the intermediate area S2 between thethrough-hole TH and the light receiving region S1 adjacent to thethrough-hole TH. The groove 13 surrounds the through-hole 111. FIG. 10and FIG. 11 are scaled differently. The size of the electrode pad 12 ofthe semiconductor photodetecting element 10F is the same as the size ofthe electrode pad 12 of the semiconductor photodetecting element 10E.

The through-holes TH and the light receiving regions S1 aretwo-dimensionally arranged. Each pitch of the through-hole TH and thelight receiving region S1 is less than those of the semiconductorphotodetecting element 10E. In the semiconductor photodetecting element10F, the through-hole TH and the light receiving region S1 are arrangedin a one-to-one relationship to achieve a higher resolution than thesemiconductor photodetecting element 10E. Each pitch of the lightreceiving region S1 and the through-hole TH is, for example, 50 μm.

The groove 13 of the semiconductor photodetecting element 10F surroundsthe through-hole TH in such a state that the grooves 13 are separated inthe row direction and the column direction in which the through-holes THare arranged. Like the groove 14 of the semiconductor photodetectingelement 10E, the groove 14 of the semiconductor photodetecting element10F also extends along two opposing sides of two adjacent lightreceiving regions S1 when viewed from the Z-axis direction. The groove14 connects the grooves 13 surrounding different through-holes TH. Inthe semiconductor photodetecting element 10F, the entire circumferenceof the light receiving region S1 is also surrounded by the grooves 13and 14.

In order to reduce the influence of the parasitic capacitance on theavalanche photodiode APD, the grooves 13 and 14 are formed in such amanner that the edges of the grooves 13 and 14 are along the edge D1 ofthe light receiving region S1. It is difficult to reduce the size of thethrough-electrode TE because of problems in machining accuracy orensuring electrical connection. In order to reduce the parasiticcapacitance generated between the electrode pad 12 and the fillingmaterial 13 a in the grooves 13 and 14, the grooves 13 and 14 areseparated from the electrode pad 12.

Under these conditions, the groove 14 is not shared by two adjacentlight receiving regions S1, and the light receiving region S1 of thesemiconductor photodetecting element 10F has a polygonal shape differentfrom the light receiving region S1 of the semiconductor photodetectingelement 10E. More specifically, the light receiving region S1 of thesemiconductor photodetecting element 10F has a polygonal shape in whichthe length of the side opposing the adjacent light receiving region S1is shorter than the length of the side opposing the adjacentthrough-hole TH.

With this configuration, in the semiconductor photodetecting element10F, the resolution is higher than that of the semiconductorphotodetecting element 10E, and the semiconductor photodetecting element10F has a higher aperture ratio. The parasitic capacitance generatedamong the avalanche photodiode APD, the filling material 13 a, and theelectrode pad 12 is reduced.

Although the preferred embodiments and modifications of the presentinvention have been described above, the present invention is notnecessarily limited to the above-described embodiments andmodifications, and various modifications can be made without departingfrom the gist thereof.

In the above-described embodiment and modifications, a single avalanchephotodiode APD is electrically connected to a single through-electrodeTE (a single electrode pad 12), but the present embodiment andmodification are not limited thereto. A plurality of avalanchephotodiodes APD may be electrically connected to a singlethrough-electrode TE (a single electrode pad 12).

In the above-described embodiment and modifications, two types of layerstructures, i.e., the semiconductor substrate 50A and the semiconductorsubstrate 50B, are illustrated as the avalanche photodiode APD, but thelayer structure of the semiconductor substrate is not limited thereto.In the avalanche photodiode APD provided in the semiconductor substrate50A, for example, the second semiconductor region 1NA and the thirdsemiconductor region 1NB may be made of a single semiconductor region.In which case, the avalanche photodiode APD includes a semiconductorregion of a first conductivity type (for example, N-type), asemiconductor region of a second conductivity type (for example, P-type)forming a pn junction with the semiconductor region of the firstconductivity type, and another semiconductor region of the secondconductivity type that is located in the semiconductor region of thesecond conductivity type and that has a higher impurity concentrationthan the semiconductor region of the second conductivity type. In thisconfiguration, the semiconductor region of the second conductivity typehaving the higher impurity concentration is the light receiving region.In the avalanche photodiode APD provided in the semiconductor substrate50B, for example, the first semiconductor region 2PA, the secondsemiconductor region 2PB, and the fourth semiconductor region 2PC may bemade of a single semiconductor region. In which case, the avalanchephotodiode APD includes a semiconductor region of a first conductivitytype (for example, P-type), and a semiconductor region of a secondconductivity type (for example N-type) that is located in thesemiconductor region of the first conductivity type and that forms a pnjunction with the semiconductor region of the first conductivity type.In this configuration, the semiconductor region of the secondconductivity type is the light receiving region.

In the semiconductor substrate 50A and the semiconductor substrate 50B,each conductivity type of P-type and N-type may be exchanged to beopposite to the above conductivity type. The light receiving region S1of the semiconductor substrate 50A may be configured to include N⁺layer, N layer, P layer, and P⁺ layer, which are arranged in this orderfrom the principal surface 1Na. The light receiving region S1 of thesemiconductor substrate 50B is configured to include P⁺ layer, N layer,N⁻ layer, N⁺ layer, which are arranged in this order from the principalsurface 1Na.

In the above-described embodiment and modifications, the distance α is5.5 μm and the distance β is 7.5 μm. The distance α and the distance βmay be other than the above values as long as the distance β is longerthan the distance α.

Although in the above-described embodiment and modifications, the lightreceiving regions S1 are described as having the polygonal shape whenviewed from the Z-axis direction, other shapes may be used. For example,the light receiving regions S1 may have a circular shape, or any othersuitable shape. Although in the above-described embodiment andmodifications, the through-holes TH are described as having the circularshape when viewed from the Z-axis direction, other shapes may be used.For example, the through-holes TH may have a polygonal shape, or anyother suitable shape.

INDUSTRIAL APPLICABILITY

The present invention can be used for a photodetecting device to detectweak light.

REFERENCE SIGNS LIST

-   1 photodetecting device-   12 electrode pad-   13, 23 groove-   13 d, 23 d bottom surface-   50A, 50B semiconductor substrate-   1Na, 1Nb principal surface-   S1 light receiving region-   S2 intermediate area-   APD avalanche photodiode-   TH through-hole-   TE through-electrode-   a, p distance-   1PA first semiconductor region-   1PB fourth semiconductor region-   1NA second semiconductor region-   1NB third semiconductor region-   2PA first semiconductor region-   2PB second semiconductor region-   2PC fourth semiconductor region-   2NA third semiconductor region-   AR1, AR2 area-   D1, D2, 13 e, 13 f edge.

1-8. (canceled) 9: A photodetecting device comprising: a semiconductorsubstrate including a first principal surface and a second principalsurface that oppose each other; a plurality of avalanche photodiodeseach including a light receiving region disposed at the first principalsurface side of the semiconductor substrate, the avalanche photodiodesbeing distributed in a matrix at the semiconductor substrate, andarranged to operate in Geiger mode; and a plurality ofthrough-electrodes electrically connected to corresponding lightreceiving regions, and penetrating through the semiconductor substratein a thickness direction, wherein at the first principal surface of thesemiconductor substrate, a groove is formed independently for each lightreceiving region to surround the light receiving region when viewed froma direction perpendicular to the first principal surface. 10: Thephotodetecting device according to claim 9, wherein, when viewed fromthe direction perpendicular to the first principal surface, an areasurrounded by the groove has a polygonal shape, and the light receivingregion has a polygonal shape. 11: The photodetecting device according toclaim 9, wherein, when viewed from the direction perpendicular to thefirst principal surface, an opening of the through-hole has a circularshape, and an insulating layer is disposed on an inner peripheralsurface of the through-hole. 12: The photodetecting device according toclaim 9, wherein the grooves formed to surround the light receivingregions adjacent to each other are separated from each other. 13: Aphotodetecting device comprising: a semiconductor substrate including afirst principal surface and a second principal surface that oppose eachother; a plurality of avalanche photodiodes each including a lightreceiving region disposed at the first principal surface side of thesemiconductor substrate, the avalanche photodiodes being distributed ina matrix at the semiconductor substrate, and arranged to operate inGeiger mode; and a plurality of through-electrodes electricallyconnected to corresponding light receiving regions, and penetratingthrough the semiconductor substrate in a thickness direction, whereinthe plurality of through-electrodes are disposed for each areasurrounded by four mutually adjacent avalanche photodiodes of theplurality of avalanche photodiodes, each of the light receiving regionshas an approximately rectangular shape when viewed from a directionperpendicular to the first principal surface, and the light receivingregions adjacent to each other oppose each other at corners of the lightreceiving regions when viewed from the direction perpendicular to thefirst principal surface. 14: The photodetecting device according toclaim 13, wherein, when viewed from the direction perpendicular to thefirst principal surface, an opening of the through-hole has a circularshape, and an insulating layer is disposed on an inner peripheralsurface of the through-hole. 15: The photodetecting device according toclaim 13, wherein at the first principal surface of the semiconductorsubstrate, a groove is formed for each light receiving region tosurround the light receiving region when viewed from the directionperpendicular to the first principal surface. 16: The photodetectingdevice according to claim 15, wherein each of the avalanche photodiodesincludes: a first semiconductor region of a first conductivity typelocated at the first principal surface of the semiconductor substrate; asecond semiconductor region of a second conductivity type located at thesecond principal surface of the semiconductor substrate; a thirdsemiconductor region of the second conductivity type located between thefirst semiconductor region and the second semiconductor region andhaving a lower impurity concentration than the second semiconductorregion; and a fourth semiconductor region of the first conductivity typeformed in the first semiconductor region and having a higher impurityconcentration than the first semiconductor region, wherein the fourthsemiconductor region is the light receiving region, and a bottom surfaceof the groove is constituted by the second semiconductor region. 17: Thephotodetecting device according to claim 15, wherein each of theavalanche photodiodes includes: a first semiconductor region of a firstconductivity type located at the first principal surface of thesemiconductor substrate; a second semiconductor region of the firstconductivity type located at the second principal surface of thesemiconductor substrate and having a higher impurity concentration thanthe first semiconductor region; a third semiconductor region of a secondconductivity type formed at the first principal surface of the firstsemiconductor region; and a fourth semiconductor region of the firstconductivity type formed in the first semiconductor region to be incontact with the third semiconductor region, and having a higherimpurity concentration than the first semiconductor region, wherein thethird semiconductor region is the light receiving region, and a bottomsurface of the groove is constituted by the second semiconductor region.18: The photodetecting device according to claim 15, wherein the groovesurrounds an entire circumference of the corresponding light receivingregion when viewed from the direction perpendicular to the firstprincipal surface. 19: The photodetecting device according to claim 15,wherein the groove formed to surround two light receiving regionsadjacent to each other shares a portion formed between the two lightreceiving regions adjacent to each other. 20: The photodetecting deviceaccording to claim 15, wherein the grooves formed to surround the lightreceiving regions adjacent to each other are separated from each other.21: The photodetecting device according to claim 15, further comprising:an electrode pad disposed on the first principal surface andelectrically connected to the through-electrode, wherein, when viewedfrom the direction perpendicular to the first principal surface, theelectrode pad is located in an area surrounded by the grooves and spacedapart from the grooves. 22: The photodetecting device according to claim15, wherein, when viewed from the direction perpendicular to the firstprincipal surface, an area surrounded by the groove has an approximatelyrectangular shape.